Hydrothermal Synthesis And Characterization Of Transition Metal Oxides Nanostructure

Nanomaterials and nanostructures have attracted great interests due to their novel physical, chemical, and biological properties as well as the potential applications in nanodevices. Hydrothermal method has been widely employed to prepare nanomaterials and nanostructures due to its advantage of low synthesis temperature, simplicity, cost-effectiveness, high crystallization, environmental friendliness and high yield.In this thesis, organic molecules assisted hydrothermal methods are used to prepare CuO nanoflowers, Co₃O₄ nanowires, litchi-like ZnO nanostructures and transition metal oxides nanoplates (e.g. Fe₂O₃, Co(OH)₂ and Ni(OH)₂) and nanospheres (e.g. Fe₂O₃, Ni and Cu). The samples synthesized are characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and so on. The primary results achieved in the thesis are listed in the following.1. Hollow flower-like CuO nanostructures were synthesized by DMF-assisted solvothermal method. The formation mechanism of such nanostructures has been preliminary presented. The lithium battery using the Flower-like CuO nanostructures as the cathode exhibited higher capacity and better cycle life than that using the conventional CuO nanoparticles as the cathode.2. The Co₃O₄ nanorods were prepared by the calcination of the cobalt-hydroxide-carbonate nanorods which were synthesized by the formaldehyde-assisted hydrothermal method. The first cycle discharge capacity of the electrodes made from Co₃O₄ nanorods was about 1540 mAh/g, and maintains about 1100 mAh/g after ten cycles.3. A novel solvothermal process using ethylene glycol (EG) as solvent has been employed to synthesize the litchi-like ZnO nanostructures consisting of the numerous ZnO nanorods with the diameter of about 50 nm and the length of about several hundred nanometers. The litchi-like ZnO nanostructures based gassensor exhibited high sensitivity for ethanol and ammonia as well as quick response and recovery time when operating at room temperatures due to the high surface-to-volume ratio of litchi-like ZnO nanostructures.4. Fe₂O₃ nanospheres were synthesized by a hydrothermal process in which formaldehyde was used as the reducing agent. During the hydrothermal process, the amorphous metal Fe nanospheres with the diameters of 20 nm were firstly formed by the reduction of Fe³⁺ ions, subsequently, they were oxidized and further grew up into Fe₂O₃ nanospheres.5. A citric acid (CA)-assisted hydrothermal process was used to prepare Fe₂O₃ hexagonal nanoplates with a lateral size of about 100 nm. In addition, the hexagonal nanoplates of Co(OH)₂, MnCO₃, and Ni(OH)₂ were also synthesized by this route, indicative of the universality of the solution route presented herein. Furthermore, the mechanism for the formation of the platelike nanostructures has been preliminarily discussed. It is believed that the capping molecule of CA, which inhibits crystal growth along the <001> direction due to its chelating effect, plays a critical role in the hydrothermal formation of the nanoplates.